1. Field of the Invention
The present invention pertains to a hydraulic control system including a valve for minimizing rapid increases in system pressure caused by the sudden application of full fluid flow to a motor or actuator.
2. Background
There are many hydraulic circuits wherein linear or rotary actuators and motors are subject to being turned on by the sudden application of full system fluid flow imposed on the motor or actuator inlet line. This sudden application of full fluid flow caused by, for example, the movement of an on-off throttling valve to the fully open position creates extremely rapid and sharp increases in system pressure imposed on the motor or actuator and the upstream hydraulic circuitry. This rapid rise in pressure, if even only momentary, repeated often enough causes fatigue failures in various parts of the system including the motor or actuator itself, the supply piping or hoses and on component parts of the load connected to the motor.
Even though most conventional hydraulic systems are provided with pressure limiting or relief valves these valves are designed to be normally in a closed condition and their operating response time is insufficient to reduce or eliminate sharp increases or spikes in system pressure between the fluid supply pump and the motor upon initiation of supplying hydraulic fluid to the motor.
The abovedescribed phenomena has been a longstanding problem in the art of hydraulic control systems and is particularly troublesome in applications wherein the duty cycle of the pump and motor includes repeated on-off operation of the motor. One example is in connection with a hydraulic motor driven fan or vacuum pump used in dust collection systems for earth drilling rigs. Since these systems are normally started and stopped in relation to drilling activity the numerous events that accompany the drilling of blastholes and other drilling operations requires a severe on-off duty cycle for the dust collection system. The cyclic operation of the vacuum pump drive motor in this application has significantly shortened the life of the motor and drive components before the discovery of the control system and valve of the present invention.
There are, of course, many other applications involving cyclic on-off loading of hydraulic motors and actuators which are subject to momentary pressure peaks at the onset of startup in the range of 2.0 to 2.5 times normal system operating pressures and wherein pressures in the system are controlled only by conventional pressure limiting valves. Systems experiencing such rapid pressure increases, however brief they may be, are subject to cyclic stresses which may materially shorten the life of system components. It is to this end that the present invention has brought a solution to a longstanding problem in the art of hydraulic motors and control systems.